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one of the methods of pressure shaping, in which the tool exerts repeated intermittent action on the stock, which as a result is deformed and acquires the desired shape and dimensions.
Since ancient times, forging of copper and native iron has been one of the main methods of metalworking (cold and later hot forging in Iran, Mesopotamia, and Egypt in the fourth and third millennia B.C.; cold forging by Indians in North and South America before the 16th century A.D.). The ancient metallurgists in Europe, Asia, and Africa forged blooming iron, copper, silver, and gold. The smiths enjoyed the special respect of the ancients, and their art was surrounded by legends. During the Middle Ages forging attained a high level in many countries, including Russia: smith forging was used in the production of weapons and firearms, tools, parts of agricultural equipment, and hardware for doors, chests, grates, lanterns, locks, clocks, and other articles of a variety of shapes and sizes, frequently containing very small parts. Forged articles were decorated with inlays, cut-out or relief patterns, and gold and bronze leaf flattened into extremely thin layers. The traditions of medieval skills were preserved in folk art until the 19th century (lanterns, hooks, candle holders, and other articles). Numerous remarkable forged lamps, fences, and gates were produced during the 15th to 19th centuries (Versailles, St. Petersburg, and Tsarskoe Selo). Many towns specialized in various branches of the blacksmith’s craft: Herat and Mosul were famous for household utensils; Damascus, Milan, Augsburg, Astrakhan, and Tula, for arms; Nottingham, Solingen, and Pavlovo na Oke, for knives and tools; and Nuremberg and Kholmogory, for locks. During the 19th century, manual artistic forging was replaced by stamping and casting, but interest in this area was revived during the 20th century (the work of F. Kühn in the GDR and of I. S. Efimov and V. P. Smirnov in the USSR; and the design of interiors of public buildings in Tallinn, Kaunas, and other cities).
The bases of the theory of forging were developed in Russia: in 1831, P. P. Añosov used a microscope for the first time in studying the structure of metals. In 1868, D. K. Chernov provided scientific substantiation of the conditions of forging. Important contributions to the theory of forging were made by the Soviet scientists N. S. Kurnakov, K. F. Grachev, S. I. Gubkin, and K. F. Neimaier.
Forging is usually performed by heating of the metal to the forging temperature to increase its plasticity and lower its resistance to deformation. The temperature range of forging depends on the chemical composition and structure of the metal being worked, as well as on the type of operation or transition. The temperature range for steel is 800°-1100°C, and for aluminum alloys it is 420°-480°C.
A distinction is made between die forging and free forging (without dies). In die forging the metal is limited on all sides by the walls of the die impression, and upon deformation it acquires the shape of the impression. In manual or mechanical free forging the metal is either not limited at all or is limited only on one side. Smith forging involves direct action on the metal or tool with a sledge or hammer. Mechanical forging is performed with special equipment, such as hammers with dropping components weighing 1–5,000 kg or hydraulic presses that develop forces of 2–200 meganewtons (MN), or 200–20,000 tons-force (tf), as well as forging machines. Forgings weighing as much as 100 tons are produced. Heavy billets are handled by cranes (with lifting capacities of up to 350 tons), turners, and special manipulators.
Free forging is used to improve the quality and structure of the metal. Forging of a metal leads to its strengthening through curing of discontinuities and reduction of the size of large crystals, which leads to the formation of a fine-grained, fibrous crystalline structure.
An assortment of blacksmith’s tools, which impart the desired shape and dimensions to the stock, are used in forging. The main forging operations are swaging, upsetting, hot drawing, peening, rolling, and broaching.
Forging is one of the most economical methods for the production of blanks. Die forging is mainly used in mass and large-batch production, and free forging is predominant in small-batch and piece production.
REFERENCESObrabotka metallov davleniem. Moscow, 1961.
Kovka iob”emnaia shtampovka stali: Spravochnik, 2nd ed, vol. 1. Edited by M. V. Storozhev. Moscow, 1967.
L. A. NIKOL’SKII
The plastic deformation of metals, usually at elevated temperatures, into desired shapes by compressive forces exerted through a die. Forging processes are usually classified either by the type of equipment used or by the geometry of the end product. The simplest forging operation is upsetting, which is carried out by compressing the metal between two flat parallel platens. From this simple operation, the process can be developed into more complicated geometries with the use of dies. A number of variables are involved in forging; among major ones are properties of the workpiece and die materials, temperature, friction, speed of deformation, die geometry, and dimensions of the workpiece.
In practice, forgeability is related to the material's strength, ductility, and friction. In terms of factors such as ductility, strength, temperature, friction, and quality of forging, various engineering materials can be listed as follows in order of decreasing forgeability: aluminum alloys, magnesium alloys, copper alloys, carbon and low-alloy steels, stainless steels, titanium alloys, iron-base superalloys, cobalt-base superalloys, columbium alloys, tantalum alloys, molybdenum alloys, nickel-base superalloys, tungsten alloys, and beryllium. See Metal
Some of the terminology in forging is shown in the illustration. Draft angles facilitate the removal of the forging from the die cavity. The purpose of the saddle or land in the flash gap is to offer resistance to the lateral flow of the material so that die filling is encouraged. Die filling increases as the ratio of land width to thickness increases up to about 5; larger ratios do not increase filling substantially and are undesirable due to increased forging loads and excessive die wear. The purpose of the gutter is to store excess metal. The flash is removed either by cold or hot trimming or by machining.
A number of methods produce the necessary force and die movement for forging. Two basic categories are open-die and closed-die forging. Drop hammers supply the energy through the impact of a failing weight to which the upper die is attached. Another type of forging equipment is the mechanical press. For large forgings the hydraulic press is the only equipment with sufficient force. However, the speed for such presses is about one-hundredth that of hammers. See Metal forming